Andersons pediatric cardiology 1911

FIG.73.14 ChestradiographyofthepatientinFig.73.13afterplacement
ofanepicardialpacemakersystemwithoneatrialandfiveunipolar
ventricularleads,oneofwhichisdisconnected.Twosetsofunipolarleads
wereplacedtoresynchronizethefunctionalsingleventriclebecauseof
ventriculardysfunction.Theatrialleadisanendocardialleadplaced
epicardially.

ImplantableCardioverter-Defibrillators
SuddendeathaftertheFontanprocedureisnotthatuncommon,12,103usually
occurringinthecontextofendstageoftheFontancirculationfailure.Itmaybe
relatedtoeventssuchaspulmonaryandcerebralembolismorpoorlycontrolled
atrialtachycardias.Implantablecardioverter-defibrillatorsareaclassIB
indicationforsecondarypreventionfollowingresuscitatedcardiacarrestdueto
sustainedVTorventricularfibrillation.111However,implantationcarriesa
significantriskinthosewithFontanfailuregiventhatitentailsthoracicsurgery.
Ifpacingisnotrequired,asubcutaneousimplantablecardioverter-defibrillator


maybeanoptioninsomepatients.112Carefulconsiderationshouldbemade
regardingdefibrillationthresholdtestingatthetimeofimplantationbecausethis
processcanbelethalinthosewithsevereventricularfailure.

AtrialTachyarrhythmias
IntraatrialReentrantTachycardias
Theassociationofatrialtachycardiaswithpooroutcomeisatleastpartly
correlatedtotheunderlyingsubstrateofthearrhythmia,ratherthanthe
arrhythmiaperse.IntheatriopulmonaryFontan,thereisanelectromechanical
correlationbetweentheoccurrenceofarrhythmiaandthedegreeofatrialdilation
andthickening.113Riskfactorsalsoincludepreviouspulmonaryartery
banding,98isomerism,andasystemicrightventricle.
TheobservationthatatrialdilatationwasassociatedwithIARTledinpartto

theadoptionofthelateraltunnelprocedure.TheprevalenceofIARThasproven
tobelowerwiththistypeofFontanconnection.98Theexternalcardiacconduit
approachreducesintracardiacsurgeryandavoidsprogressivedilationofthe
atrialwall,butitisnotevidentthatthisoperativestrategyisassociatedwitha
reducedprevalenceofIARTcomparedwiththelateraltunnel.
InvasiveelectrophysiologicstudiesdemonstratethatthemechanismofIART
commonlyinvolvessurgicalscarscreatedduringsuturingofthelateral
tunnel.114–116Thesestudiesreveallargeareasoflow-voltagediseasedatrial
myocardium,withfractionatedsignalsdemonstratingdelayedand
nonhomogeneouselectricalconduction.Thissubstrateisidealforthe
developmentofintraatrialreentry(Fig.73.15).113,114


FIG.73.15 (A)ECGdemonstratingintraatrialreentranttachycardiaina
53-year-oldfemalewithtricuspidatresiawhounderwentamodifiedFontan
withrightatriumtorightventriclevalvedconduit.TheredarrowsmarkP
waves.(B)Intracardiacelectrogramsofthesamepatientdemonstratinga
secondinducibleintraatrialreentranttachycardiafollowingsuccessful
ablationofthetachycardiaseeninFig.73.11A.Therewasanareaofslow
conductioninthesuperiorrightatriumwithlowamplitude,fractionated
signalsbestdepictedintheT2positionofamultielectrodecatheter(red
arrows).Successfulablationwasperformedatthissite.Notealsothe
diffuselowvoltage/absentsignalsatotherelectrodesonthisscarred
atrium.

Atrialreentrycircuitdependsonareasofslowconductionindiseasedatrial
myocardiumwithelectricallysilenttissueoneachside.Thisresultsinaslow
conductingbridge,oristhmus.Anelectricalsignalenterstheisthmus,andbythe
timetheelectricalsignalisreleasedfromthisisthmus,thehealthymyocardium
isabletoconductagain;thesignalpropagatesaroundtheatriumandbacktothe